This Phase II/III, randomized, comparative, double-blind, three-arm, outpatient, multicenter study is designed to determine the comparative effectiveness of 3TC/ZDV versus the better of ddI monotherapy versus ZDV/ddI combination therapy with respect to HIV disease progression. Seven hundred ten symptomatic, HIV-1-infected infants and children aged 90 days to 15 years will be enrolled in this study nationwide. Participants will be randomized to one of three treatment arms: 1) oral 3TC and ZDV, 2) oral ddI; or 3) oral ddI plus ZDV. Subjects will be treated for 24 months from date of last patient randomization, or until the study is terminated. The primary objective of this study is to compare the efficacy of treatment with 3TC/ZDV in combination versus the better of ddI monotherapy versus ddI/ZDV combination therapy. Results will be determined by HIV disease progression based on the time to development of the first new CDC Category C diagnoses, or death, or failure to achieve adequate weight growth velocity, or decline in neuropsychological or neurological assessments. We are in a relatively early phase of this study. The study medications, however, appear to be well-tolerated.